Only a subset of MGE neuronal derivatives maintain Nkx2-1 and Lhx8 expression, such as the globus pallidus and cholinergic striatal interneurons (Marin et al., 2000), whereas MGE-derived cortical interneurons suppress Nkx2-1 and Lhx8 expression (Nóbrega-Pereira et al., 2008). We propose that Dlx and Nkx2-1 pathways interact at this step. We demonstrated that Dlx1/2 were required for Zfhx1b expression in the subpallial SVZ (Figure 4), and that Zfhx1b was required for repression of Nkx2-1, but not of Lhx8 (Figures 2D-F’, 2M-O’, 3A-C’ and 3J-L’). Thus, in the absence of Zfhx1b, dorsal MGE-derived neurons continued to express Nkx2-1, Sox6 and Lhx6, and migrate into the striatum and not the cortex. These cells failed to express markers of cortical interneurons (Cxcr7, cMaf and MafB) (Figures 7 A-L”, S5A-S5I’), but highly expressed the striatal GABAergic subtype markers NPY, nNos and Sst. (Figures 2P-R’ and 3M-O’ (Tepper et al., 2010). Additionally, there was increased expression of TacR1, which is robustly expressed in Sst+ and ChAT+ striatal interneurons, and in very few cortical interneurons (Ardelt et al., 1996; Figure S4D-S4F’).
